NNadir
NNadir's JournalConspiracy: As if the Ghost... ...was me.
Laser Cooling of Antihydrogen.
The paper to which I'll point in this post is this one: Laser cooling of antihydrogen atoms (Baker, C.J., Bertsche, W., Capra, A. et al. Laser cooling of antihydrogen atoms. Nature 592, 3542 (2021))
Beyond an inordinate interest in neutrons, I'm not much for deeper particle physics. My kid won a medal in the 5th grade science project for a poster on the subject and some of the other parents of kids in the competition accused me of doing the project, but to be perfectly honest, I actually had no idea what he was talking about.
Nevertheless, chemists are aware that on a molecular level life is asymmetric, and one theory that's floated by my consciousness from time to time is the asymmetry of beta decay of neutrons (the Wu experiment) was involved in the mysterious origins of molecular asymmetry. As I understand it, this has been difficult to prove.
I am also vaguely aware that physicists have wondered why the universe seems to have excess matter, that is, why wasn't as much antimatter created as matter was created.
Antimatter can be prepared in the laboratory, and positrons are actually pretty easy to get: Proton bombardment of stable nuclei yields, upon proton capture, neutron poor atoms that decay by positron emission. When positrons interact with electrons, they are annihilated, releasing intense gamma radiation.
The paper cited at the outset is about isolated anti-hydrogen, a hydrogen atom with an anti-proton with a positron (an anti-electron) in its orbital; not only has it been synthesized, but it has been supercooled, which makes this a cool paper or perhaps an anti-cool paper.
Happily, it is open sourced, and anyone can read it by clicking on the link above.
Some excerpts:
Doppler cooling, the type of laser cooling used in this work, takes place via the velocity-dependent absorption of near-resonant photons by atoms. The atoms moving towards the photon source are selectively excited by setting the photon frequency slightly below the resonance for the atom at rest (red detuning), resulting in a net force opposing the motion2,3. The spontaneous emission of a photon from the excited atom occurs in a spatially symmetric manner in free space, resulting in a null average recoil force. In the case of (anti)hydrogen26, by exciting the 1S2P Lyman-? transition, a net velocity change of 3.3 m s?1 can be exerted on average by each 121.6-nm photon scattered. In principle, repeating such scatterings only a few dozen times should slow (anti)hydrogen atoms, initially trapped in a well depth of about 50 ?eV (corresponding to a maximum speed of about 90 m s?1), down to submicroelectronvolt energies.
In practice, however, laser cooling of antihydrogen presents a number of technical challenges. First, generating and transporting radiation at 121.6 nm is difficult. There are no convenient lasers or nonlinear crystals at vacuum ultraviolet wavelengths, and the light is readily attenuated in air and in optical components...
A picture:
Fig. 1: The ALPHA-2 apparatus schematic and antihydrogen energy levels.
The caption:
Cool/Anti-cool.
Have a nice weekend, and if you are a Christian, happy Easter.
"I am resonant...organic chemistry taught me to fully inhabit my mixed identities."
I came across this quote the other day in my Nature Briefing:
When I really take a moment to see these bonds for what they area union of atoms in three dimensionsI also witness my sense of self, split between mixed identities, scooch to a sweet spot in the center that is a space all its own.
Science writer Ariana Remmels moving personal essay considers how organic chemistry helped to illuminate the complexities of their racial and gender identity.
It links here:
"I am resonant...organic chemistry taught me to fully inhabit my mixed identities."
This is just a beautiful piece of writing.
Some excerpts:
My brother has just turned one. He toddles with the help of my mothers hand. Normally, she would have dressed him in a swim diaper that swells like a balloon once he submerges in the kiddie pool. Today, Mom has put him in a pair of baby-blue swim trunks.
I want to wear swim trunks, I tell my mother.
Swim trunks are for boys, honey. You get to wear a one-piece. She is curt because my brother is crying. He has thrown his chupón onto the concrete and she is trying to find a clean one.
But I want to wear swim trunks.
Sweetie, girls have to cover up. You cant walk around bare chested. Its just not right. She is trying to be reasonable, but my brother has begun to remove the swim trunks altogether...
...I hate going to church. Dad never comes, so it is just me, my siblings, and my mother at St. Edwards Cathedral. The Mass is entirely in Spanish. I do not speak Spanish. No one speaks Spanish to me...
Mom tried to teach us when we were little, but I am twelve now and Ive learned to hate the sound of it. It is the sound of a priest who tells me that a womans hair is her glory. I...
...I am cramped into one of those chairs with a tiny desk that slides out, used for standardized tests. This is one of the big onesa college-admissions test that will decide my future. But I am stuck on the very first page. Sex: Female or Male. I check Female with some remorse, but I still dont have the words to describe my sadness. Race: White, Black, Latino, Pacific Islander, Asian. The instructions say to check one. Only one.
When I look in the mirror, I think I look white. That is, until I gaze into my dark-brown eyes, which are my mothers and my Litas and her mothers before her. I have my fathers pale skin and my mothers round features. If I choose white, no one will bat an eye. I will only feel the guilt of erasing my mother and abuelos and the sacrifices they made for me to be here...
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